Pulmonary venous flow reversal in mitral regurgitation
Dogs and cats with significant mitral regurgitation (MR) may show pulmonary venous flow reversal. Flow reversal is a supporting measure only, and not specific enough to be used as a standalone method of grading MR severity.
Normal pulmonary vein flow pattern
The normal flow pattern of the pulmonary veins shows two forward-flowing waves – systolic (S) and diastolic (D). The S wave should be of equal or greater velocity than the D wave. There is also a small reversal wave (Ar) that occurs at the time of atrial contraction. This is present even in normal cats and dogs, but becomes more pronounced with diastolic dysfunction. With mitral regurgitation, however, we are most interested in the S wave.
How the S wave velocity changes with significant mitral regurgitation
S wave blunting can occur in any situation where there are elevated left atrial pressures, so this includes diastolic dysfunction and (rarely encountered) mitral stenosis as well as mitral regurgitation, which is why it is not specific to MR.
In severe MR or where the regurgitant jet is directed down the pulmonary vein, blunting can be even more pronounced and there may even be S wave reversal, as below:
Obtaining your trace
In mild mitral regurgitation, a normal pulmonary vein inflow pattern would be expected. Systolic blunting may be seen in moderate MR, and systolic reversal in severe MR (Zoghbi et al., 2003).
It is not always possible to obtain a pulsed wave Doppler profile of reversal in the pulmonary veins if the velocity of flow exceeds your scale. You can attempt to increase your pulse repetition frequency (PRF) by:
- Reducing your Doppler frequency in order to produce a smaller Doppler shift
- Switching into high PRF mode – this may lead to some range ambiguity, which you will be alerted to by the presence of a second Doppler gate, but as long is this gate is not over an area with significant blood flow then it should not interfere with your trace.
Sometimes, it is possible to appreciate the backflow of blood down the pulmonary veins even with colour Doppler.
Zoghbi, W., Enriquez-Sarano, E., Foster, P. et al. (2003). American Society of Echocardiography: recommendations for evaluation of the severity of native valvular regurgitation with two-dimensional and Doppler echocardiography. European Journal of Cardiovascular Imaging.
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